Today I had a fitting for the 915 D2 driver.  My current driver is a 910 D2, 10.5 degrees with a stiff adila RIP alpha shaft.  We tried a few shafts at the fitting but the best numbers were with the Adila Rogue SIlver (110 MSI) 60 X Stiff in a 9.5 degree head to keep the spin rate down at around 3,100 RPM.  Based on the fitting, the fitter has recommended I actually go for the 70 X Stiff instead to reduce spin/dispertion further but he didn't have one to trial today.  

I've looked at a lot of articles on line this afternoon and based on every one there's no way my 100 mph swing speed should be compatible with an X stiff shaft.  Does anyone on the forum have any explanation for what seems to be an outcome that is at odds with science!?